1. Field of the Invention
This invention relates to electronic time keeping devices, and in particular to a new and improved means and method for adjusting the frequency of operation of an electronic time keeping device.
2. Description of the Prior Art
Time keeping devices, which employ electronic circuitry for providing electrical signals to indicate the correct time, are known in the art. In a typical device, an extremely stable high frequency oscillator supplies time base signals or pulses. These signals are divided down by known circuitry which supplies a signal train of pulses having a frequency of 1 Hz. This signal train is coupled to a time keeping unit comprising a number of counters which are incremented by the 1 Hz pulses. A scale of 60 counter provides a count representative of the correct second of the minute. Another scale of 60 counter provides a count representative of the correct minute of the hour. A scale of 12 counter provides a count representative of the correct hour of the day. In some devices, additional counters are included to provide a count representative of the day of the month, day of the week, and month of the year.
The outputs of the time keeping unit counters are decoded, and typically are coupled to a multidigit liquid crystal or light emitting diode display means. As the counters are clocked to different states by the 1 Hz clock pulses, the decoded outputs are supplied either directly, or indirectly by means of an enabling display switch, to the display means, thereby providing a visual output indicating the time.
Time keeping systems of the above type provide a degree of accuracy which surpass conventional mechanical movements, primarily due to the high frequency time base employed and the excellent frequency stability of electronic digital circuitry. Also, fully electronic systems are less expensive to manufacture than mechanical systems, and exhibit a much longer lifetime since there are no moving mechanical parts. However successful development of smaller and lower cost electronic watches, which also maintain a high degree of accuracy, has been impeded by the use of such components as a variable capacitor and a quartz crystal for stablizing the base signal at a precise frequency.
The typical prior art electronic wristwatch employs a quartz crystal as a means for stablizing the frequency of oscillation of the base signal generating oscillator. Further, since quartz crystals can only stabilize the frequency of oscillation within a reasonable range of frequencies, a pair of capacitors are typically employed with the oscillator to further adjust and stablize the frequency of oscillation. One of these capacitors is generally fixed and the second is variable. After assembly of an electronic wristwatch module the variable capacitor must be precisely adjusted to cause the oscillator to generate the precise frequency of oscillation desired. Needless to say, this operation is time consuming, and if it becomes necessary to readjust the frequency of oscillation after some period of time, the wristwatch must be returned to someone having the proper equipment to make this adjustment. Furthermore, the capacitors consume critical space within the wristwatch and they are costly components.
Another costly and space consuming component of the typical prior art electronic wristwatch module is the quartz crystal. Though some means of stablizing the frequency of oscillation of the base signal generation is required, other means may be provided as set forth in greater detail hereinbelow.